The invention relates generally to work vehicles having power shift transmissions. More particularly, it relates to automated methods for calibrating the clutches in the power shift transmissions using removable calibration tools.
Power shift transmissions are commonly used in a variety of work vehicles ranging from road graders to agricultural tractors. As the term is generally used in the construction and agricultural equipment industries, a power shift transmission is a transmission that can be shifted from gear ratio to gear ratio without significantly reducing the power output of the transmission during the shift.
In order to do this, the transmissions are arranged with several internal shafts that are each equipped with one or more hydraulic clutches. These clutches are typically multi-plate xe2x80x9cwetxe2x80x9d clutches that are immersed in hydraulic fluid. To change from gear ratio to gear ratio, one or more clutches are disengaged substantially simultaneously with the engagement of one or more additional and different clutches by introducing fluid into the clutches being engaged at the same time fluid is released from the clutches being disengaged.
Unlike a typical manual mechanical shift transmission in which there is one clutch located outside of the transmission which engages and disengages the engine from the transmission, and wherein manual manipulation of the shift lever causes gears to slide on shafts within the transmission in order to effect the gear change, a power shift transmission connects or disconnects gears by locking them or unlocking them to the corresponding shafts by the engagement and disengagement, respectively, of their corresponding clutches. Generally speaking, in a full power shift transmission all of the gears are always in mesh. What shifts the transmission is the locking and unlocking of particular gears to their corresponding shafts.
One of the benefits of this arrangement is that the time required to disengage the transmission from one gear ratio and engage the transmission in another gear ratio is significantly reduced. A gearshift in a power shift transmission can occur in as little as fifty or one hundred milliseconds.
One danger in this shifting process is that of wear or damage to internal parts. As one set of clutches is disengaged and another set is engaged, at some point all the clutches may be simultaneously engaged. This can cause serious damage to the transmission as gear teeth break, or extreme wear as the clutches are forced to slip with respect to each other. Alternatively, if neither the gears break or the clutches slip, simultaneous engagement in two gear ratios can bring the engine to a sudden and precipitous stop. This is called xe2x80x9cfour-squaring the transmissionxe2x80x9d.
The opposite danger is that of being disengaged from any gear ratio for too long. If the power shift transmission is on a tractor pulling a sixteen-bottom plow through a field, for example, and if the gear shifting permits the vehicle to be disengaged from the engine for a half a second or a second, the tractor may stop completely due to the extreme load before the new gear ratio is engaged. Once stopped, it may be necessary to shift down to the lowest gear ratio to start the tractor moving again. This would effectively prevent the tractor from being used in any of the higher gear ratios when a large load is on the tractor.
For this reason, the timing of clutch engagement and disengagement is of critical importance when shifting. To accurately coordinate the engagement and disengagement of the clutches, it is necessary to determine the amount of time between the operator""s command to the clutches to engage or disengage and to use this information to xe2x80x9cschedulexe2x80x9d shifts. By xe2x80x9cschedulingxe2x80x9d I refer to the process of using the time delay between the time a command is given to an electronic valve controlling fluid flow to a clutch and the time that clutch is actually filled with fluid and begins to engage to determine the proper times of clutch valve energization and de-energization.
Determining the time delay between applying an electrical signal to a clutch valve and the corresponding clutch engagement or disengagement is not a trivial task, nor, for most vehicles can it be measured once and stored in an electronic memory for perpetual use.
As the hydraulic components of the work vehicle wear, the time delay (also known as the xe2x80x9cclutch fill timexe2x80x9d) can vary, sometimes dramatically. For this reason, it is important that the clutch fill time be periodically re-measured and stored in the electronic circuitry that schedules the transmission shifts. In some applications, such as when small engines are used in demanding applications it may be necessary to determine the clutch fill times of the clutches on an almost continuous basis. In this case, the work vehicle is usually equipped with several clutch fill time sensors that are permanently attached to the electronic circuitry and re-measure the clutch fill times for each clutch as the vehicle actually works in the field. For other vehicles, this continual clutch fill time calibration may not be necessary.
If clutch fill time calibration is only necessary every few weeks or few months, it may be possible to reduce the complexity of the electronic circuitry and reduce the cost of the work vehicle by configuring the electronic circuitry of the work vehicle to automatically interact with a maintenance person or operator and with a removable clutch calibration service tool that are together capable of determining the clutch fill time and saving the clutch fill time in the electronic circuitry.
By providing a removable service tool that need only be connected to the work vehicle electronic circuitry every few months during the calibration process, the cost of the vehicle could be reduced by several hundred dollars. It is an object of this invention to provide such a system and method.
In accordance with a first embodiment of the invention, a method for calibrating hydraulic clutches in a powershift transmission of a work vehicle is provided which includes the steps of manually connecting a pressure transducer to a first hydraulic fluid conduit extending between a first clutch control valve and a first clutch in the powershift transmission such that the pressure transducer generates an electronic pressure signal indicative of the fluid pressure in the first clutch, manually connecting the pressure transducer to an electronic transmission controller on the vehicle, wherein the electronic transmission controller is configured to drive the pressure transducer and to receive the electronic pressure signal, electronically signaling the first clutch valve to fill the first clutch with hydraulic fluid, electronically monitoring the time required to fill the first clutch, recording a digital value indicative of the time required to fill the first clutch in an electronic memory of the electronic transmission controller, manually disconnecting the first pressure transducer from the first conduit, and manually disconnecting the first pressure transducer from the electronic transmission controller.
The step of manually connecting to a first conduit may include the step of fluidly coupling the first pressure transducer to a quick-connect coupling mounted on the transmission. The pressure transducer may be electrically connected to a first electrical connector such that the transducer and connector together define a removable and replaceable structure and further wherein the step of connecting to the controller includes the step of coupling the first electrical connector to a mating electrical connector on the work vehicle, wherein the mating electrical connector is electrically coupled to the electronic transmission controller. The step of electronically monitoring may include the step of comparing a digital value indicative of a current clutch pressure signal provided by the pressure transducer with a digital value indicative of at least one past clutch pressure signal provided by the pressure transducer. The step of comparing may include the step of determining that the digital value indicative of a current clutch pressure signal is greater than the digital value indicative of at least one past clutch pressure signal by a predetermined pressure difference. The step of electronically storing may include the steps of calculating a digital elapsed time value in the electronic transmission controller indicative of the elapsed time from the step of electronically signaling to the time of the step of determining, and saving the digital elapsed time value in the electronic transmission controller. The method may include the step of subtracting a predetermined time interval from the digital elapsed time value to generate a reduced digital elapsed time value, and saving the reduced digital elapsed time value in the electronic transmission controller. The step of purging the first clutch, prior to the step of electronically signaling the first clutch valve, may be implemented by electronically energizing, then deenergizing, then energizing, and then deenergizing the solenoid of the first clutch valve. The step of electronically monitoring may include the steps of waiting a predetermined time interval for a fill pressure of the first clutch to stabilize, recording a digital value indicative of the stabilized fill pressure, reading a new pressure signal from the first pressure transducer, comparing the stabilized fill pressure with the new pressure signal, and repeating the steps of reading a new pressure signal and comparing the stabilized fill pressure until the new pressure signal exceeds the stabilized fill pressure signal by a predetermined pressure difference.
In accordance with a second embodiment of the invention, a method of calibrating a plurality of clutches in a powershift transmission with a pressure transducer is provided, including the steps of manually connecting a pressure transducer to a first hydraulic conduit that extends from a first clutch control valve to a first hydraulic clutch in the transmission to provide an electronic pressure signal indicative of the fluid pressure in the first clutch, manually connecting the pressure transducer to an electronic transmission controller on the vehicle, wherein the electronic transmission controller is configured to receive the pressure signal, electronically signaling the first clutch valve in a clutch valve manifold to fill the first clutch with hydraulic fluid, electronically monitoring the time required to fill the first clutch, recording a first digital value indicative of the time required to fill the first clutch in an electronic memory of the electronic transmission controller, manually disconnecting the pressure transducer from the first hydraulic conduit, manually connecting the pressure transducer to a second hydraulic conduit that extends from a second clutch control valve to a second hydraulic clutch in the transmission to generate an electronic pressure signal indicative of the fluid pressure in the second clutch, electronically signaling the second clutch valve in the clutch valve manifold to fill the second clutch with hydraulic fluid, electronically monitoring the time required to fill the second clutch, recording a second digital value indicative of the time required to fill the second clutch in the electronic memory of the electronic transmission controller, manually disconnecting the pressure transducer from the second hydraulic conduit, and manually disconnecting the pressure transducer from the electronic transmission controller.
The steps of manually connecting may include the step of fixing the pressure transducer to quick-connect couplings, and the steps of manually disconnecting may include the step of removing the pressure transducer from the quick-connect couplings. The step of electronically signaling the first clutch valve may include the step of manually signaling the electronic transmission controller that the pressure transducer is fluidly coupled to the first clutch, and the step of electronically signaling the second clutch valve may include the step of manually signaling the electronic transmission controller that the pressure transducer is fluidly coupled to the second clutch.
In accordance with a third embodiment of the invention, a method of automatically calibrating the fill time of a plurality of hydraulic clutches in a powershift transmission of a work vehicle using a test instrument comprised of at least first and second electronic pressure transducers electrically coupled to the inputs of a switch box, the switch box having an electrical output switchably connectable to at least the first and second pressure transducers is provided, including the steps of fluidly connecting the first transducer to a hydraulic fluid supply line of a first hydraulic clutch of the plurality of clutches, fluidly connecting the second transducer to a hydraulic fluid supply line of second hydraulic clutch of the plurality of clutches, coupling the output of the switch box to an electronic controller of the work vehicle, selecting the first pressure transducer at the switch box to thereby electrically couple the first pressure transducer to the electronic controller, manually indicating to the electronic controller that the first transducer has been selected, electronically determining the fill time of the first clutch using the first transducer, selecting the second pressure transducer at the switch box to thereby electrically couple the second pressure transducer to the electronic controller, manually indicating to the electronic controller that the second transducer has been selected, and electronically determining the fill time of the second clutch using the second transducer.
The step of fluidly connecting the first pressure transducer may include the step of connecting the first pressure transducer to a first quick-connect coupling. The step of fluidly connecting the second pressure transducer may include the step of connecting the second pressure transducer to a second quick-connect coupling. The quick connect coupling may be mounted on a transmission shaft bearing end cap. The end cap may define a cap hydraulic line that communicates hydraulic fluid to a shaft hydraulic fluid line machined in a transmission shaft supported in the transmission. The quick connect coupling may be mounted on a clutch valve manifold that includes a plurality of electronically actuated clutch control valves for controlling a corresponding plurality of flows of hydraulic fluid to corresponding plurality of clutches in the transmission. The first clutch control valve may be one of the plurality of valves.